Recommendations for Assessment

As previously mentioned, all stormwater treatment practice assessment programs should include regularly scheduled visual inspections (level 1) at least once per year. Capacity testing (level 2) and synthetic runoff testing (level 3) are techniques to evaluate specific functions of a stormwater treatment practice with relative accuracy. They can be used to determine how performance of a stormwater treatment practice is changing with respect to time, changes in the watershed, or both. If the goals of the assessment program cannot be met by capacity testing or synthetic runoff testing, or these techniques are not feasible, then monitoring (level 4) should be considered as part of the assessment program. Monitoring is the most comprehensive assessment technique and will assess stormwater treatment practice performance within the watershed without modeling. One must, however, be ready to accept more uncertainty in the results because performance is more difficult to assess due to the variability of natural rainfall events, discharge and pollutant concentration during monitoring. Table 3.1 summarizes the four levels of assessment and the advantages and disadvantages of each level.